1. Field of the Invention
The present invention relates to a reading apparatus for simultaneously reading image data printed on both sides of a document. More particularly, this invention is concerned with a reading apparatus, serving as an input means, for simultaneously reading printed image information from both sides of a document storing the read image information on a recording medium such as an optical disk.
2. Description of the Related Art
In recent years, the advance of computer technology has accelerated the trend towards the paperless office where information is stored on recording media including magnetic and optical disk but not on paper. To keep up with this trend towards the paperless office, an input unit, to convert printed information on a document into digital data storable in a recording medium such as an optical disk, is needed. The input unit is available as an image scanner.
To use an image scanner, a document is placed on a glass plate, referred to as a flat bed, a cover is closed, and then a switch is pressed. Light from a light source and an image detecting device is scanned across the bottom of the glass plate, whereby the image data is read. This kind of image scanner makes it necessary to turn over a document printed on both sides of paper to read the entire document. It is therefore slow and inconvenient to read the image data. To improve the image data input rate, there is an increasing demand for a reading apparatus capable of reading printed image data from both sides of a document during a single scan.
In general, this kind of reading apparatus has a built-in automatic carrier mechanism. In the middle of the automatic carrier mechanism, a front data reader for reading the front of a document and a back data reader for reading the back of the document are located. When a document having both sides thereof printed with information is inserted into the reading apparatus, through a slot, the document is carried in the apparatus by means of the carrier mechanism. When the document passes the front data reader, image data is read from the front of the document by means of the surface data reader. Next, when the document passes through the back data reader, image data is read from the back of the document by means of the back data reader. Each of the surface and back data readers has a sensor that detects a leading edge and a trailing edge of a document. When the sensor detects a leading edge of a document, the front data reader or back data reader starts reading the image data. When the sensor detects a trailing edge of the document, the front data reader or back data reader terminates reading.
In the conventional reading apparatus for reading two sides of a document, either of the sensors for detecting the leading and trailing edges of a document may malfunction due to dirt and dust and reduce the detecting efficiency. This results in unstable detection of a trailing edge of a document. When trailing-edge detection for a document becomes unstable, although a trailing edge of a document does not pass the sensor, the sensor recognizes that the document has passed. Before the whole of the document is read, image data reading terminates. In this case, read data is not complete.